Ethanol can be made in two ways.
Method 1 is fermentation: C6H12O6(aq)→2C2H5OH(aq)+2CO2(g)\mathrm{C_{6}H_{12}O_{6}(aq)} \rightarrow \mathrm{2C_{2}H_{5}OH(aq)} + \mathrm{2CO_{2}(g)}C6H12O6(aq)→2C2H5OH(aq)+2CO2(g)
Method 2 is the hydration of ethene: C2H4(g)+H2O(g)⇌C2H5OH(g)\mathrm{C_{2}H_{4}(g)} + \mathrm{H_{2}O(g)} \rightleftharpoons \mathrm{C_{2}H_{5}OH(g)}C2H4(g)+H2O(g)⇌C2H5OH(g)
The table gives some information about the two methods.
| Feature | Method 1 | Method 2 |
|---|---|---|
| raw material | sugar from crops (renewable) | ethene from crude oil (non-renewable) |
| conditions | 30 °C, 1 atm, yeast | 300 °C, 60 atm, phosphoric acid catalyst |
| type of process | batch | continuous |
| rate | slow | fast |
| product | dilute solution of ethanol (about 15 %) | about 95 % pure ethanol |
Calculate the atom economy of method 1. Relative formula masses: C2H5OH=46,CO2=44\mathrm{C_{2}H_{5}OH} = 46, \mathrm{CO_{2}} = 44C2H5OH=46,CO2=44
State the atom economy of method 2 and give a reason for your answer.
In method 2, only about 5 % of the ethene is converted into ethanol each time the gases pass through the reactor. Explain how the overall yield can still be high.
Use the table to give two advantages of method 1 compared with method 2.
A company needs large amounts of pure ethanol quickly. Explain which method it should choose.
51 exam-style questions on Edexcel GCSE Chemistry 6.2 Quantitative analysis, covering 6.2.1 Concentration in mol dm⁻³ and titration calculations, 6.2.2 Percentage yield and why actual yield falls short, 6.2.3 Atom economy of a reaction, 6.2.4 Choosing a reaction pathway, and 6.2.5 Molar volume of gases and Avogadro's law. Each one has a worked solution and a mark scheme showing where the marks go.